Pulsed DC Voltage Research Articles

Phase Transformation of TiO2 Thin Films in Function Bias Voltage

Titanium dioxide thin films have been deposited on silicon (100) and 316L stainless steel substrates by cathodic arc deposition in oxygen atmosphere with a titanium cathode. The process was run at room temperature and at 300°C, biasing the substrate with pulsed voltage (up to –10kV) and DC voltage (up to –120V). The crystalline structure was studied by Raman spectroscopy and X-ray diffraction. At room temperature, the films were obtained with an amorphous base with small isolated crystals of rutile and anatase. At 300°C, with DC bias, samples grew crystalline with the presence of both anatase and rutile.

Effect of additive oxygen gas on cellular response of lung cancer cells induced by atmospheric pressure helium plasma jet.

The atmospheric pressure helium plasma jet driven by pulsed dc voltage was utilized to treat human lung cancer cells in vitro. The properties of plasma plume were adjusted by the injection type and flow rate of additive oxygen gas in atmospheric pressure helium plasma jet. The plasma characteristics such as plume length, electric current and optical emission spectra (OES) were measured at different flow rates of additive oxygen to helium. The plasma plume length and total current decreased with an increase in the additive oxygen flow rate. The electron excitation temperature estimated by the Boltzmann plot from several excited helium emission lines increased slightly with the additive oxygen flow. The oxygen atom density in the gas phase estimated by actinometry utilizing argon was observed to increase with the additive oxygen flow. The concentration of intracellular reactive oxygen species (ROS) measured by fluorescence assay was found to be not exactly proportional to that of extracellular ROS (measured by OES), but both correlated considerably. It was also observed that the expression levels of p53 and the phospho-p53 were enhanced in the presence of additive oxygen flow compared with those from the pure helium plasma treatment.

Effect of Pulse Rise time on Plasma Plume Propagation Velocity

Atmospheric pressure plasma jets driven by a pulsed dc power supply have several advantages over the traditional jets driven by an ac power supply. However, how the pulse rise time affects the characteristic of the plasma jets is not clearly known. In this paper, the simulation results of a plasma jet driven by pulsed dc voltages with different pulse rise time trise are presented. It shows that, the shorter the pulse rise time trise is, the faster the head of the plasma jet propagates.

Dual Three-Pulse Modulation-Based High-Frequency Pulsating DC Link Two-Stage Three-Phase Inverter for Electric/Hybrid/Fuel Cell Vehicles Applications

This paper proposes a new modulation technique dual three-pulse modulation (DTPM) to switch dual full-bridge output capacitorless dc/dc converters to develop a pulsating dc link voltage encoding six pulse rectified output information. The pulsating voltage is directly fed to a standard six-pack inverter to develop three-phase ac output voltage. Proposed inverter and modulation are suitable for electric, hybrid electric, and fuel cell vehicles. The absence of the dc link capacitor and DTPM produce pulsating dc voltage that retains the sine-wave information (six- or three-phase rectified output) at the input of three-phase inverter. Inverter devices are modulated for 33% (one-third) of the line cycle and remains in their unique switching state (either on for 33% or off for 33%) and results in average device switching frequency of one-third of switching frequency. This results in 66% savings in switching losses. In addition, devices are not switched when the current through them is at its peak value and total savings in switching loss accounts to be up to 86.7% in comparison with a standard voltage source inverter with sine pulsewidth modulation. This paper presents operation and analysis of the pulsating dc link two-stage inverter controlled by the proposed DTPM at the front end and 33% modulation for the six-pack inverter along with the implementation. Design of the two-stage three-phase inverter has been illustrated. Analysis has been verified through simulation results using PSIM 9.0.4. Experimental results on a lab prototype have been demonstrated to validate the claims and the proposal.

Voltage pulsing for performance recovery of yttria-stabilised zirconia membranes in oxygen/sulfur dioxide separation

The regeneration of yttria-stabilized zirconia (YSZ) membranes exposed to high concentration sulfur dioxide in oxygen at 850 °C using DC voltage pulses was investigated by in-situ impedance spectroscopy. The membranes consisted of a dense YSZ layer as the solid electrolyte coated with two platinum layers as electrodes. On operation in the presence of SO2, the serial resistance and polarization resistance of the Pt/YSZ cell increased. This is most likely due to the formation of sulfide at the interface area of the electrode and electrolyte combined with sulfur adsorption on electrode surface. DC Voltage pulses were found to have an effect on the charge transfer and mass transfer properties of the Pt/YSZ cell, assisting the removal of sulfur on the cathode surface and leading to performance recovery of the cell. In these experiments, the greatest rate of membrane performance recovery is achieved with a cathodic DC bias of 10 V, applied for 0.08 s. Higher or longer voltage pulses may cause the rate controlling step for the oxygen reduction reaction to shift to oxygen supplied in feed from oxygen surface exchange and diffusion processes. A relatively steady membrane performance was achieved during 20 h SO2 exposure tests. It is concluded that DC voltage pulses show promise as a method for reducing the performance degradation effects of poisoning due to sulfur containing gases in the fields of fuel cells and in the sulfur family of thermochemical cycles.

One-step electrochemical fabrication of bilayered MgO/polymer coating on magnesium alloy

This research demonstrates a novel one-step electrochemical method to fabricate thick bilayer coatings on magnesium alloy in acid phosphate electrolyte containing aniline monomer and styrene-acrylic emulsion (SAE) with pulsed DC voltage. The morphologies, XRD and FTIR results show that the bilayer coating consists of an inner oxide layer and an outer polyaniline (PANI)/SAE composite layer. It is believed that the bilayered structure achieved results from a hybrid process combining electropolymerization (EPM) of aniline, electrophoretic deposition (EPD) of SAE and plasma electrolyte oxidation (PEO) of magnesium alloy substrate. Electrochemical corrosion tests indicate that the bilayer coating can provide superior corrosion protection to the magnesium alloy substrate in 3.5 wt.% NaCl solution.

Plasma exposure inducing crystallization of indium oxide film with improved electrical and mechanical properties at room temperature

A novel plasma exposure technique has been introduced into conventional magnetron sputtering process to enhance the crystallization of indium oxide (In2O3) films at room temperature. The effect of plasma exposure technique with different pulsed DC voltages on the electrical and mechanical properties of In2O3 films was investigated. It is observed that film crystallization can be significantly enhanced when the pulsed DC voltage (|V p|) is higher than |−500 V| (|V p| > |−500 V|). By applying the plasma exposure process, In2O3 films prepared at room temperature with thickness of 135 nm shows low resistivity of 4.11 × 10−4 Ω cm, mobility of 42.1 cm2/Vs, and transmittance over 80 % in the visible range. Compared with the In2O3 films without plasma exposure process, the In2O3 films with plasma exposure show better crystallization and remarkably higher nanohardness. The plasma exposure technique is a useful candidate technique for enhancing film crystallization at low temperature.

Two Factors Failure Model of Oil-Paper Insulation Aging under Electrical and Thermal Multistress

Converter transformers play important roles in high-voltage direct current transmission systems. This paper presents experimental and analysis results of the combined electrical and thermal aging of oil-impregnated paper at pulsating DC voltages. Breakdown voltages and time-to-breakdown of oil-paper specimens were measured by using short-time and constant-stress tests. The breakdown characteristics of combined electrical and thermal aging on insulation system were discussed. According to the relationship between failure time and aging temperature, the two-parameter Weibull model was improved. On the basis of the competing risk algorithm and the improved Weibull model, the two factors failure model was calculated. And the influence of temperature in the insulation system has been analyzed. This model performs better than the two-parameter Weibull model when both time and temperature are considered as variables in estimating the lifetime of oil-paper insulation.

Deposition of Vulcan XC-72 Coatings on Stainless Steel Bipolar Plates by Reverse Pulsed DC Voltage Electrophoretic Deposition (EPD) for Fuel Cell Applications

In this study, surface coatings of a mixture of Vulcan XC-72 and Polypyrrole (PPy), labeled as PPy-C, were deposited on stainless steel (SS) substrates by EPD under reverse pulsed DC voltage in order to study the corrosion protection. The Effect of applied voltages (50, 70, 90 and 120 V) and deposition time (2, 6, 10 and 15 min) on the film characteristics was evaluated. The coatings were analyzed by SEM, and the result showed that the amount of PPy electrodeposited and the morphology of the film depended on the conditions of deposition. Polarization curves were conducted in order to evaluate the corrosion resistance of the bipolar plates in 0.1 M H2SO4 at room temperature. The experimental results indicated that the PPy-C composites increased the corrosion potential of the SS and decreased the corrosion current density by one order of magnitude. The structure properties of the coatings were characterized by Fourier Transform Infrared Spectroscopy (FTIR), and the spectra shows the presence of characteristics absorption bands of PPy. These results indicated that EPD is a suitable technique to deposit polymer/carbon corrosion protection films for applications in fuel cell bipolar plates.

Construction and identification of the recombinant vector silencing peroxisome proliferator-activated receptor-γand expressing calcitonin gene-related peptide gene

Objective To construct the recombinant vector silencing peroxisome proliferator-activated receptor-γ (PPARγ) and expressing calcitonin gene-related peptide (CGRP) gene.Methods The pGFP-V-RS vector we selected contains a small interfering RNA (siRNA) expressing unit,and also can express exogenous gene inserted.The PPARγ siRNA oligonucleotides sequence was ligated into pGFP-VRS vector after annealling,and then PPAR siRNA recombinant vector (pGFP-V-RS-siPPARγ) was obtained by restriction analysis and DNA sequencing.The CGRP gene fragment was ligated into linear plasmids pGFP-V-RS-siPPARγrecombinant vector,and then the recombinant vector pGFP-V-RS-siPPARγ-exCGRP was obtained by restriction analysis and DNA sequencing.The HEK-293 cells were collected and divided into 4 groups at random.In control group,the cells were only transfected with vector pGFP-V-RS plasmid.In SI group,the cells were transfected with recombinant vector pGFP-V-RS-siPPARγplasmid.In EX group,the cells were transfected with recombinant vector pGFP-V-RS-exCGRP plasmid.In DOU group,the cells were transfected with pGFP-V-RS-siPPARγ-exCGRP plasmid.There were 5 × 106 HEK-293 cells in electrode cup of each group,and 2.5 μl above-mentioned plasmids were added respectively.The cells were given DC voltage pulse one time (15 ms).The cells were harvested in each group after culture for 48 h,and CGRP and PPARγmRNA and protein expression levels were detected by using reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting.Results The results of restriction analysis and DNA sequencing were completely matched with those of the designed sequences after the PPARγsiRNA oligonucleotides sequence and CGRP gene fragment were cloned into pGFP-V-RS vector.After recombinant vector pGFP-V-RS-siPPARγ-exCGRP was transfected into HEK-293 cells,the expression levels of PPARγ mRNA and protein were reduced in DOU group DOU (0.036 ±0.003 and 0.108 ±0.031)as compared with EX group (0.156 ±0.014 and 0.778 ±0.103) and control group (0.148 ±0.014 and 0.742 ± 0.143) (P ＜ 0.05),but showed no significant difference in comparison to SI group (0.054 ± 0.005and 0.135±0.039) (P＞0.05).The expression level of CGRP mRNA and protein was significantly increased in DOU group (1.144 ±0.106 and 1.244 ±0.184) as compared with IS group (0.320 ±0.030 and 0.370 ±0.089) and control group (0.444 ±0.041 and 0.274 ±0.062) (P ＜0.05),but there was no significant difference in comparison to EX group (1.021 ±0.095 and 1.221 ±0.181) (P ＞0.05).Conclusion We successfully constructed the recombinant vector pGFP-V-RS-siPPARγ-exCGRP that silencing PPARγand expressing CGRP gene,and the recombinant vector can efficaciously suppress PPARγgene expression and promote CGRP gene expression simultaneously. Key words: RNA interference; Peroxisome proliferator-activated receptor-γ; Calcitonin generelated peptide; Recombinant vector

DC-pulsed voltage electrochemical method based on duty cycle self-control for producing TERS gold tips

This paper presents a modified dc-pulsed low voltage electrochemical method in which a duty cycle is self tuned while etching. A higher yield of gold tips suitable for performing tip-enhanced Raman scattering (TERS) measurements is demonstrated. The improvement is caused by the self-control of the etching rate along the full surface of the tip. A capability of the gold tips to enhance a Raman signal is exemplified by TERS spectroscopy of single walled carbon nanotubes bundle, sulfur and vanadium oxide.

Electrical aging lifetime model of oil-impregnated paper under pulsating DC voltage influenced by temperature

Main insulation of windings connected with valves in high voltage direct current (HVDC) convert transformers withstands pulsating DC voltages. This paper presents breakdown properties of oil-impregnated paper under pulsating DC voltages at different temperatures. Progressive stress tests were carried out to obtain breakdown voltages of oil-impregnated paper with thickness of 0.2 mm under pulsating DC voltages at different temperatures. Constant stress tests were executed to measure time to breakdown of the oil-paper specimens. Both types of the experiments were also undertaken under either AC or DC voltages. An electrical aging lifetime model was proposed for the oil-impregnated paper, and parameters of the electrical aging lifetime model were presented. Experiments and analysis results show that the breakdown voltages and time to breakdown of oil-paper insulation are influenced by temperature significantly.

A Novel Single-Reference Six-Pulse-Modulation (SRSPM) Technique-Based Interleaved High-Frequency Three-Phase Inverter for Fuel Cell Vehicles

This paper presents a hybrid modulation technique consisting of singe-reference six-pulse-modulation (SRSPM) for front-end dc/dc converter and 33% modulation for three-phase inverter. Employing proposed novel SRSPM to control front-end dc/dc converter, high frequency (HF) pulsating dc voltage waveform is produced, which is equivalent to six-pulse output at 6× line frequency (rectified 6-pulse output of balanced three-phase ac waveforms) once averaged. It reduces the control complexity owing to single-reference three-phase modulation as compared to conventional three-reference three-phase SPWM. In addition, it relives the need of dc-link capacitor reducing the cost and volume. Eliminating dc link capacitor helps in retaining the modulated information at the input of the three-phase inverter. It needs only 33% (one third) modulation of the inverter devices to generate balanced three-phase voltage waveforms resulting in significant saving in (at least 66%) switching losses of inverter semiconductor devices. At any instant of line cycle, only two switches are required to switch at HF and remaining switches retain their unique state of either ON or OFF. Besides, inverter devices are not commutated when the current through them is at its peak value. Drop in switching loss accounts to be around 86.6% in comparison with a standard voltage source inverter (VSI) employing standard three-phase sine pulse width modulation. This paper explains operation and analysis of the HF two-stage inverter modulated by the proposed novel modulation scheme. Analysis has been verified by simulation results using PSIM9.0.4. Experimental results demonstrate effectiveness of the proposed modulation.

Deposition of Vulcan XC-72 Coatings on Stainless Steel Bipolar Plates by Reverse Pulsed DC Voltage Electrophoretic Deposition (EPD) for Fuel Cell Applications

not Available.

Comparison of the characteristics of atmospheric pressure plasma jets using different working gases and applications to plasma-cancer cell interactions

Atmospheric pressure plasma jets employing nitrogen, helium, or argon gases driven by low-frequency (several tens of kilohertz) ac voltage and pulsed dc voltage were fabricated and characterized. The changes in discharge current, optical emission intensities from reactive radicals, gas temperature, and plume length of plasma jets with the control parameters were measured and compared. The control parameters include applied voltage, working gas, and gas flow rate. As an application to plasma-cancer cell interactions, the effects of atmospheric pressure plasma jet on the morphology and intracellular reactive oxygen species (ROS) level of human lung adenocarcinoma cell (A549) and human bladder cancer cell (EJ) were explored. The experimental results show that the plasma can effectively control the intracellular concentrations of ROS. Although there exist slight differences in the production of ROS, helium, argon, or nitrogen plasma jets are found to be useful in enhancing the intracellular ROS concentrations in cancer cells.

Nanopatterning and tuning of optical taper antenna apex for tip-enhanced Raman scattering performance

This paper focuses on finding optimal electrochemical conditions from linear sweep voltammetry analysis for preparing highly reproducible tip-enhanced Raman scattering (TERS) conical gold tips with dc-pulsed voltage etching. Special attention is given to the reproducibility of tip apex shapes with different etchant mixtures. We show that the fractional Brownian motion model enables a mathematical description of the decaying current kinetics during the whole etching process up to the cutoff event. Further progress in preparation of highly reproducible smooth and sharp tip apexes is related to the effect of an additive, such as isopropanol, to aqueous acids. A finite-difference time-domain method based near-field analysis provides evidence that TERS performance depends critically on tip orientation relative to a highly focused laser beam. A TERS based criterion for recognizing gold tips able to couple/decouple optical near- and far-fields is proposed.

Charge-based Delivery of Molecules to Skin Using Atmospheric Plasmas

We report the design, development and characterization of new atmospheric plasma-based protocols currently being examined in vivo using small animal models. Previously developed electric field mediated drug and gene delivery protocols use a pulsed DC voltage applied between electrodes on or in tissue to generate the required electric field to induce delivery of molecules. Plasma sources deliver roughly a million times less charge to skin compared with direct electrode-driven delivery methods, yet the efficiency of the process is dramatically similar with respect to the introduction of molecules to skin cells.

Nanomaterials Processed by Spark Plasma Sintering

The spark plasma sintering (SPS), a variant of field-assisted sintering (FAST) or pulsed electric current sintering (PECS), is a novel pressure assisted pulsed electric current sintering process, which utilizes ON-OFF DC pulse energizing. Due to the repeated application of an ON-OFF DC pulse voltage and current flow between powder particles, the spark discharges and the Joule heating (local high temperature state) are therefore dispersed to the overall specimen.The SPS process is based on the electrical spark discharge phenomenon and is a high efficient, energy saving technique with a high heating rate and a short holding time. The problem of rapid grain growth of nanomaterials during conventional sintering can be inhibited to a larger extent by using the SPS technique. The SPS can be used for diverse novel bulk material applications, but it is particularly suitable for the processing of nanomaterials. Despite such anticipated advantages, the optimization of the process window (heating rate-temperature-time) in SPS process is a challenging task. More importantly, the underlying mechanisms for superfast densification still remains to be explored.

High temperature oxygen separation for the sulphur family of thermochemical cycles – Part II: Sulphur poisoning and membrane performance recovery

The effect of sulphur dioxide (SO2) present in the cathode feed stream on the performance of an 8 mol% yttria-stabilized zirconia/Platinum (8YSZ/Pt) cell was studied. SO2 concentration of 30% in oxygen (5 ml/min) and helium (30 ml/min) was exposed to the cell applying an external DC voltage of 1.5 V at 850 °C. Experiments showed that the cell performance, inferred from current and oxygen permeate flux changes, had two types of degradation. The first was rapid, giving a sharp fall (type I degradation) and the second much more gradual (type II degradation). The presence of Platinum sulphide (PtS) was observed after the SO2 exposure period using X-ray diffraction (XRD), scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDX) and Raman spectroscopy. The cell performance was partially recovered after a 2 min DC voltage pulse treatment. The results of XRD, EDX and Raman analysis indicated that the recovery may be attributed to the removal of the sulphide layer from the cathode surface after the voltage pulse treatment. The greatest recovery of cell performance was obtained after a 2 min pulse of 4.5 V. Preliminary investigations on the effect of a much shorter, 1 s voltage pulse on performance recovery were conducted and recovery was found to increase up to the highest voltage tested, 7 V.

Numerical prediction of the electrical waveform effect on electrocoalescence kinetic

The effect of external electric field characteristics on the binary water droplet coalescence in stagnant oil has been studied using Computational Fluid Dynamics (CFD) simulations. Volume of Fluid (VOF) approach is applied as a multiphase model, in which the hydrodynamic equations consisting of Navier–Stokes and interface tracking equations are solved using finite volume discretization scheme. Dipole-induced-dipole (DID) model is utilized to calculate the electrostatic force on water droplets. Different types of electrical waveforms have been implemented using appropriate potential functions. The studied electrical voltages are sine, triangle, sawtooth, pulsed DC, and bipolar square waveforms. The predicted kinetic for electrocoalescence is in good agreement with the experimental data of the literature. The results demonstrated that a bipolar square wave provided the most efficient waveform, while sine and pulsed DC voltages gave lower efficiencies due to the time variation and off-time intervals, respectively. Triangle and sawtooth waveforms produced the least efficient waveforms. In addition, the effect of frequency has been studied for the aforesaid electrical waveforms in the adopted binary drop system. No significant differences have been proved in the approaching time of the drops from the studied frequencies. The results revealed that the electric fields with higher value of root mean squares (RMS) result in more efficient electrocoalescences. Furthermore, it was manifested that the higher voltage amplitude in every waveform improves this phenomenon.